Influence of flow conditions and system geometry on nitrate use by benthic biofilms: implications for nutrient mitigation

Iron mediated autotrophic denitrification for low C/N ratio wastewater: A review

In recent years, iron mediated autotrophic denitrification has been a concern because it overcomes the absence of organic carbon and has been successfully used in denitrification for low C/N ratio wastewater. However, there is currently a lack of a more systematic summary of iron-based materials that can be used for denitrification, and no detailed overview about the mechanism of iron mediated autotrophic denitrification has been reported. In this study, the iron materials with different valence states that can be used for denitrification were summarized, and emphasized, as well as the mechanism in different interaction systems were emphasize. In addition, the contribution of various microorganisms in nitrate reduction were analyzed and the effects of operating conditions and water quality were evaluated. Finally, the challenges and shortcomings of the denitrification process were discussed aiming to find better practical engineering applications of iron-based denitrification.

Community-level and function response of photoautotrophic periphyton exposed to oxytetracycline hydrochloride

Periphyton is considered important for removal of organic pollutants from water bodies, but knowledge of the impacts of antibiotics on the community structure and ecological function of waterbodies remains limited. In this study, the effects of oxytetracycline hydrochloride (OTC) on the communities of photoautotrophic epilithon and epipelon and its effect on nitrogen and phosphorus concentrations in the water column were studied in a 12-day mesocosm experiment. The dynamics of nitrogen and phosphorus concentrations in the epipelon and epilithon experiment showed similar patterns. The concentrations of total nitrogen, dissolved total nitrogen, ammonium nitrogen, total phosphorus and dissolved total phosphorus in the water column increased rapidly during the initial days of exposure, after which a downward trend occurred. In the epilithon experiment, we found that the photosynthesis (Fv/Fm) and biomass of epilithon were significantly (P < 0.05) stimulated in the low concentration group. Contrarily, growth and photosynthesis (Fv/Fm) were significantly (P < 0.05) reduced in the medium and high concentration group. We further found that the photosynthetic efficiency of photoautotrophic epilithon was negatively correlated with the concentrations of nitrogen and phosphorus in the water column (P < 0.05). Principal coordinate analysis (PCoA) showed that the communities of epilithic algae in the control group and in the low concentration group were significantly (P < 0.05) different from that of the high concentration group during the initial 4 days. After 8 days' exposure, all groups tended to be similar, indicating that epilithon showed rapid adaptability and/or resilience. Similar results were found for the relative abundance of some epilithic algae. Our findings indicate that the biofilm system has strong tolerance and adaptability to OTC as it recovered fast after an initial suppression, thus showing the important role of periphyton in maintaining the dynamic balance of nutrients with other processes in aquatic ecosystems.

Role and application of iron in water treatment for nitrogen removal: A review

It is crucial to have a review on the role of iron in water treatment for the guidance towards the selection of appropriate processes, content of iron, and application conditions, as there are few reviews available at present and the systematic information is lacking for both researchers and engineers. The objectives of this review are to summarize the state of arts with respect to iron applied in nitrogen removal, discuss chemical and biological or bio-chemical combined nitrogen removal pathways and processes coupled with iron, and to reveal reaction mechanisms as well as providing references or even solutions to pertinent the practical engineering application of nitrate removal coupling with iron. The following information have been summarized and discussed in details: (1) iron based materials with varieties of preparations and forms, (2) major coupling ways of nitrogen removal methods or processes with iron application, (3) chemical reaction equations about a variety of chemical and biological or bio-chemical combined processes and the main mechanisms. In addition, challenges and/or drawbacks during the nitrogen removal processes will also be discussed in this paper, which is aimed to seek better practical engineering applications of nitrate removal coupling with iron.

Nitrogen Removal and N2O Accumulation during Hydrogenotrophic Denitrification: Influence of Environmental Factors and Microbial Community Characteristics

Hydrogenotrophic denitrification is regarded as an efficient alternative technology of removing nitrogen from nitrate-polluted water that has insufficient organics material. However, the biochemical process underlying this method has not been completely characterized, particularly with regard to the generation and reduction of nitrous oxide (N₂O). In this study, the effects of key environmental factors on hydrogenotrophic denitrification and N₂O accumulation were investigated in a series of batch tests. The results show that nitrogen removal was efficient with a specific denitrification rate of 0.66 kg N/(kg MLSS·d), and almost no N₂O accumulation was observed when the dissolved hydrogen (DH) concentration was approximately 0.40 mg/L, the temperature was 30 °C, and the pH was 7.0. The reduction of nitrate was significantly affected by the pH, temperature, inorganic carbon (IC) content, and DH concentration. A considerable accumulation of N₂O was only observed when the pH decreased to 6.0 and the temperature decreased to 15 °C, where little N₂O accumulated under various IC and DH concentrations. To determine the microbial community structure, the hydrogenotrophic denitrifying enrichment culture was analyzed by Illumina high-throughput sequencing, and the dominant species were found to belong to the genera Paracoccus (26.1%), Azoarcus (24.8%), Acetoanaerobium (11.4%), Labrenzia (7.4%), and Dysgonomonas (6.0%).

Effects of the combination of aeration and biofilm technology on transformation of nitrogen in black-odor river

Excess nitrogen in urban river networks leading to eutrophication has become one of the most urgent environmental problems. Combinations of different aeration and biofilm techniques was designed to remove nitrogen from rivers. In laboratory water tank simulation experiments, we assessed the removal efficiency of nitrogen in both the overlying water and sediments by using the combination of the aeration and biofilm techniques, and then analyzed the transformation of nitrogen during the experiments. Aeration (especially sediment aeration) combined with the biofilms techniques was proved efficient in removing nitrogen from polluted rivers. Results indicated that the combination of sediment aeration and biofilms, with the highest nitrogen removal rate from the overlying water and sediments, was the most effective combined process, which especially inhibited the potential release of nitrogen from sediments by reducing the enzyme activity. It was found that the content of dissolved oxygen in water could be restored on the basis of the application of aeration techniques ahead, and the biofilm technique would be effective in purifying water in black-odor rivers.

Impact of streambed morphology on the abundance and activity of ammonia-oxidizing bacteria

Ammonia oxidizers catalyze the first step of nitrification. Combined microbial nitrification-denitrification activities are essential for the removal of excess nitrogen from water bodies. In sandy streambeds, bed form structures are created by water flow and lead to the creation of heterogeneous microenvironments. The objective of this study, therefore, was to investigate the effect of bed form morphology on the abundance and activity of ammonia-oxidizing bacteria (AOB) within a benthic biofilm. An 8-month-old benthic biofilm was established in a recirculating laboratory flume under controlled flow conditions and frequent amendment with ammonium. The sand bed was arranged into bed form structures. The highest concentrations of chlorophyll a (indicative of algae) were measured on the upstream side of the bed forms. The biofilm was dominated by Nitrosospira species, and amoA gene abundance was higher on the downstream sides of the bed forms with no significant difference in oxygen consumption between the upstream and downstream sections of the bed form. In contrast, potential ammonium oxidation rates were higher on the upstream sides of the bed forms. The results suggest that bed form morphology can affect the spatial distribution and activity of AOB, possibly through the creation of distinct microhabitats. These results contribute to our understanding of nitrogen transformations and removal from streams.